Home repossessions at Northern Rock are running at twice the rate registered before the bank was nationalised in February, according to figures analysed by the Guardian yesterday.

The Newcastle-based lender repossessed more than 400 homes in May out of its securitised mortgages, compared with less than 118 in December and 237 in January, showing the bank is taking a more aggressive stance on mortgage arrears since it was taken into public ownership.

While rival banks have also increased the rate at which they repossess customers' homes, Northern Rock remains an industry frontrunner. Lloyds TSB, which sells mortgages through its Cheltenham & Gloucester subsidiary, took back control of 21 homes in April out of its own securitised mortgage programme.

The lenders pledge a certain proportion of their higher quality loans to securitisation and bond programmes, which are sold to outside investors. Northern Rock has 376,000 home loans in its securitisation plan, while Lloyds counts 406,000 mortgages. This is only a portion of the two banks' overall home loans portfolio.

A spokesman for Northern Rock said: "We cannot comment on the current numbers of homes in possession. But the credit quality of our mortgages are in line with our business plan."

Northern Rock is under pressure from the government to repay a £25bn loan to the exchequer following its rescue last year. Ron Sandler, chairman, said he would need until 2011 to turn around the bank's finances and repay the loan. He is expected to make 2,000 of the lender's 6,000 staff redundant and shrink the £100bn mortgage book to less than £50bn.

Yesterday it announced a three-year tie-up allowing Lloyds TSB to offer mortgages to Northern Rock customers when their deal with the lender runs out.

However, critics said Lloyds TSB was in the driving seat and would only pick the loans that it wanted from Northern Rock's books.